Automatic emergency alert system



NOV. 1961 c. T. STRATTON ET AL 3,009,059

AUTOMATIC EMERGENCY ALERT SYSTEM 2 Sheets-Sheet 1 Filed Dec. 23, 1959RECEIVER Clell T. S'rroflon FIGURE 2 Alton E. Surge INVENTORS.

BY kg 5 Nov. 14, 1961 c. 1'. STRATTON ET AL 3,009,059

AUTOMATIC EMERGENCY ALERT SYSTEM Filed Dec. 25, 1959 2 Sheets-Sheet 2FIGURE 3 IN V EV TORS.

United States Patent 3,009,059 AUTOMATIC EMERGENCY ALERT SYSTEM Clell T.Stratton, Belford, N.J., and Alton E, Sarge, El

The invention described herein may be manufactured and used by' or forthe United States Government for governmental purposes without thepayment of any Toy-- alty thereon. n

The present invention relates to; an alert system which can be used:in'conjunction with the present Conelrad alert system administered bythe Civil Defense Authorities. Under the Conelrad system the FederalCommunications Commission has designated the radio frequencies of 6 40kc. and 1240 kc. as emergency frequencies and all transmitting stationsin the alert area are instructed to switch to these frequencies in caseof an alert. These stations will then broadcast instructions tothe-populace. As presently planned, it is necessary to awaken thepopula'ce with a siren or other warning device to enable-them to tunetheir radioreceivers to one of the emergency frequencies.

The present invention provides an automatic method of warning allpersons who are within hearing distance of a radio receiver by utilizinga receiver that is auto matically activated and tuned to an emergencyfrequency when the local transmitting station switches to the emergencyfrequency. This operation will occur regardless of whether the receiveris. being operated and is therefore especially useful to alert those notlistening to their radio receivers. i

It is accordingly an object of this invention to provide an inexpensive,extensive and convenient warning system.

Another object of this invention is to provide an alert system which can'be incorporated into systems already in operation. i

An additional object of this invention is to provide an ale-rt systemwhich will operate continually. and automatically. I

A further object of this invention is to provide an alert system thatwill effectively alert a very large portion of the populace without theuse of extensive or elaborate equipment. 1 1

Other and further objects and features of the present invention willbecome apparent upon a careful consideration of the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIGURE 1 is a functional representation of the invention showing some ofthe circuit details thereof.

FIGURE 2 is a detailed drawing of the switch assembly illustrating thevarious switch positions.

FIGURE 3 is a detailed circuit diagram of a particular embodiment of theinvention.

FIGURE 1 illustrates a typical radio receiver such as a superheterodynereceiver, a TRF receiver or a PM receiver incorporating the presentinvention. The antenna A intercepts the radio frequency signal andpresents it to the radio receiver. The variable condenser C representsthe tuning condenser of the receiver which operates in conjunction witha tuning coil L to select any frequency desired. In accordance with thepresent invention an additional variable condenser C, is inserted inparallel with tuning coil L. C, is tuned to the emergency frequency andoperates in conjunction with the switch T and the tuning coil L toselect the emergency frequency when desired. The tuning circuit L-Cshown in FIG- URE 1 is representative of all the tuned radio frequencycircuts in the receiver. If the receiver uses more than I I us. Code1952 266) onetuning coil and condenser combination, a condenser C and aswitch T should be used for each such combination. For. example, thesuperheterodyne receiver shown in FIGURE 3 utilizes an additionalcondenser O 'and a switch. T; for the oscillator circuit which furnishesthe beat frequency. a 3 For convenience the power'switch T is alsoconstructed with 'four positions so it may be'ganged with the othersections of the. switch T shown in FIGURE 2. The power switch can be anordinary O'n-Oif switch or any other means for controlling the currentand any such modification is determined by the design factors concerned.

The output from the audio power tubeof the receiver is connected totheprimary of an audio output transformer 0. The secondary oftransformer O is connected to the. receiver speaker S through the relaycontact points 1 and 2 of the: relay K. The output of the audio powertube is also connected to a filter circuit comprised of R C ,-C and RThe values for these 'filter components are chosen to allow only onespecific low frequency alerting signal to activate the relay coil K Thedetector D serves to convert the alternating current from the filtercircuit to a direct current to operate the relay K. R and C are chosenwith theproper time constant to prevent undesirable transient effects inthe relay The switch T is connected to K and ground as shown and also tothe B+ of the receiver through a resistor R The relay K is a double polesingle throw type where in energization of the coil K forces contacts 1and 2 together and also forces contacts} -and 4 together. Additionalcontacts may-be provided on therelayto control lights, bells or otherinstruments which may? be necessary in conjunction with the alertsystem. A pair of additional contacts Sand 6 are illustrated in FIGURE 1and the relay shown therein is a triple, pole single throw tylm The fourpositions ofthe switch T. are illustrated in FIGURE 2,. The Playposition permits operation of the receiver in the usual manner. The Ofliposition disconnects the-power from the receiver. 7 When the switch .Tis in the Standby position the speaker circuit will be open until analerting signalis broadcast. Then the'relay K is energizedand thereceiveris putinto operation to receive the emergency instructions. Ifthe switch is set in the Playi position. when an alerting signal 'isbroadcast it will be necessary to change to the Test position to receiveemergency instructions. Under the present Conelrad system notificationof an emergency will be broadcast by all transmitting stationsimmediately so there should be no undue delay in switching from the Playposition to the Test position on switch T.

Switch T is an ordinary four position ganged switch. The number of decksor sections required will depend on the number of tuning sections in thereceiver. The superheterodyne receiver circuit shown in FIGURE 3requires four decks for proper operation. The switch T shown in FIGURE 2has four switching positions, but a switch with three positions willsuflice if the oif position is omitted and some other means are used tocontrol the power to the receiver. More than four positions can be usedto incorporate any additional well known features in the device.

The operation of the present invention when T is in the Standby positioncan best be illustrated by referring to FIGURE 1 wherein the switches TT and T are shown in the Standby position. Before broadcasting emergencyinstructions the transmitting stations will broadcast an alerting signalfor a short period of time. This alerting signal will be a low frequencyalternating signal modulated upon an emergency frequency carrier. Thetuning circuits of the receiver will receive this signal and deliver itto other circuits in the receiver for ampli- 'fication and detection.The'condenscr C must be tuned beforehand to form a resonant circuit withthe tuning coil l. at the emergency frequency to properly select theemergency signal.

The rectified and amplified low frequency alerting signal passes throughthe filter composed of R C C and R; which rejects all frequencies butthis alerting signal fre quency. This signal is applied to the RCnetwork composed of R and C which is used in conjunction with K; toactuate the relay. When K is energized contacts 1 and 2 are joined andthe speaker S is connected in para allcl with the secondary of the audiooutput transformer O. The receiver can now receive and reproduce anyemergency instructions by the transmitting station.

Since the low frequency alerting signal is only transmitted for a shortperiod of time a holding current for the relay is provided by the B+ ofthe receiver, This voltage is connected to the relay coil K through thedropping resistor R and the relay contact points 3 and 4. When thealerting signal energizes the coil K points 3 and 4 are joined as arepoints 1 and 2. Therefore a permanent energizing current is furnished tothe relay coil K even after the low frequency alerting signal hasstopped.

FIGURE 3 illustrates a practical application of the principles of thepresent invention in a snperheterodyne receiver. For a low frequencyalerting signal of 1000 I cycles per second the values of the filtercomponents can be calculated by well-known methods. These values are:

C and C =.01 f. I C R and R are chosen to properly operate the relay K.The values of L and and C can be calculated with the well-known LCresonance circuit. equations for a frequency of 1000 cycles per second.The choice of tubes and the values of the other components shown aremerely design factors and need not be considered extensively here.

Various modifications and alterations of the invention which have beendisclosed herein are possible. The device could be made portable and canbe extended to cover spirit and scope of the invention as defined in theappended claims.

We claim: 1'. In a single radio receiver-including a speaker, an

automatic emergency alert system comprisingmeans for receiving modulatedradio frequency signals and isolating the modulating voltages therefrom,and an audio output stage having an audio transformer, said systemcomprising relay means having a pair of normally open contact points anda relay coil connected to said points for causing the points to move toa closed position upon the energizing of said relay coil, said contactpoints being electrically connected to the secondary of said outputtector and said relay coil to prevent undesirable transientotheremergcncies such as floods. tornadoeshurricanes or effects in saidrelay; and a power switch means having a plurality of operatingpositions including a Standby position in which the receiver isconnected to a source of electrical power whereby a low frequencyalerting signal is received and passed through said filter and appliedto said RC network to actuate said relay coil whereby said pair ofcontacts are closed, a Play positionin which said relay coil isenergized to place said speaker in the circuit for normal listening, aTest position in which said relay coil is not energized unless theemergency alerting frequency is received and permits adjustment of thereceiver to the alerting frequency signal, and an Off position in whichsaid relay coil is shorted by said switch and the receiver placed in aninoperative condition.

2. The device as in claim 1 wherein there is provided a droppingresistor, a second pair of normally open switch contacts connected intosaid-source of power applied to said receiver, said relay coil alsoconnected into said power source through said dropping resistor and saidsecond pair of contacts whereby a holding current is established forsaid relay coil.

References Cited in the file of this patent UNITED STATES PATENTS1,833,986 Christofiel Dec; '1, 1931- 2,330,241 Roberts Sept. 28, 19432,353,499 Purington July 11, 1944 2,617,923 Rekart Nov. 11, 19522,630,564 Gibson Mar. 3, 1953 OTHER REFERENCES A Co'nelrad Monitor byOliphant, Radio & TelevisionNews, January 1955, page 99.

